A Study on Check Helms for Course Keeping of a Ship under Steady External Forces

Among various aspects of manoeuvrability of ships, steerability in wind, wave, and current is one of the vitally important problems, because it is directly related to the safety of ship handling. To this steerability, rudder operations for course keeping, which are usually called as “check helms”, are closely related.Investigation was made, therefore, on a calculation method of check helms for course keeping under steady external forces. This method is derived so as to fully utilize captive model test results for assured reliability.As an example ship form, a liquified natural gas carrier (LNGC) was examined. With the results of captive model tests, check helms and drifting angles were calculated for various design requirements which include estimation of the effects of rudder area and drifting forces due to wind and wave, together with their full-scale prediction. And it was shown that the present method is one of the practical and useful calculation methods.